Bearing force hierarchized reinforcing RC pier and design method thereof

Abstract

To provide a bearing force hierarchized reinforcing RC pier and a design method thereof, in which a function of a bridge is hardly damaged even against a maximum earthquake motion, while securing aseismatic performance against a design earthquake motion for an existing RC pier.SOLUTION: A bearing force hierarchized reinforcing RC pier 20 has an existing RC pier, an RC wound-up reinforcing part 23, a bearing force hierarchized reinforcing bar 24 to which a bearing plate 24a is fixed on the upper end side, and a hollow sheath 25. The hollow sheath 25 is formed as a hollow part for housing the bearing force hierarchized reinforcing bar 24 on the upper side in a loosely fitted state, the upper part side is formed as a large hollow part 25a, the lower surface part of the large hollow part 25a is abutted on the lower surface of the bearing plate 24a to form a tensile resistance surface resisting tensile force, and the large hollow part 25a is formed at a height position exceeding a plastic hinge section of a column part 2b. An expansion gap is formed between the bearing plate 24a and the tensile resistance surface in a normal time, and an expansion gap length dx is formed so as to satisfy a predetermined conditional formula.SELECTED DRAWING: Figure 8

Description

[Technical field]

[0001] The present invention relates to a strength-hierarchical reinforced RC pier in which strength is hierarchically structured according to the intensity of earthquake motion, and a design method thereof. [Background technology]

[0002] The design earthquake motion stipulated in Specifications for Highway Bridges V (Japan Road Association: Specifications for Highway Bridges, Commentary V, Earthquake-Resistant Design, 2017) takes into consideration two levels of earthquake motion based on past earthquake motion characteristics, namely, earthquake motion with a high probability of occurring during the bridge's service life (Level 1 earthquake motion), and earthquake motion with a low probability of occurring during the bridge's service life but with great strength (Level 2 earthquake motion). For Level 2 earthquake motion, two types are taken into consideration: Type I earthquake motion, which assumes a large-scale earthquake motion at a plate boundary, and Type II earthquake motion, which assumes an inland earthquake. However, the possibility of an extremely large earthquake occurring that exceeds the design earthquake motion cannot be denied. Therefore, road bridges are required to ensure seismic performance against the design earthquake motion while maintaining as little loss of functionality as possible even in the event of the extremely large earthquake motion.

[0003] Conventionally, proposed earthquake-resistant design methods for two levels of earthquake motion intensity include placing outer and inner main rebars within a concrete structure and fixing the ends of the inner main rebars to the concrete structure with an axial gap, or placing a compressible member at the lower end of the inner main rebar that activates the inner main rebar after the compression or tension allowance is eliminated, thereby providing the bridge pier with a reinforced concrete structure that activates when subjected to strong earthquake motion (see Patent Documents 1 and 2). However, in these proposals, it is unclear how to set the axial gap and the compression and tension allowances of the compressible member, and since the extremely large earthquake motion that exceeds the design earthquake motion is not assumed, there is a problem that the seismic performance against the extremely large earthquake motion cannot be satisfied. In other words, if the axial gap and the compression allowance of the compressible member are set short, when the extremely large earthquake motion is received, the inner reinforcing bar together with the outer reinforcing bar will start to operate with an external force less than the design earthquake motion, and the deformation capacity of the pier will not be fully exerted, and members other than those assumed in the design may be damaged, and the bridge may not perform as expected. Also, if the axial gap and the tension allowance of the compressible member are set long, the pier may collapse before the inner reinforcing bar operates. Furthermore, there is a risk that the ultimate displacement will be exceeded in the event of the extremely large earthquake motion mentioned above, and it cannot be denied that the bridge piers will collapse. Since earthquake resistance performance is ensured up to the above-mentioned design earthquake motion through the earthquake-resistant design of the Highway Bridge Specifications V, what is now required is earthquake-resistant design against the above-mentioned extremely large earthquake motion.

[0004] Incidentally, in addition to newly constructed bridge piers, existing bridge piers naturally also require seismic design to withstand such extremely large earthquake motions. It is not realistic to demolish the vast number of existing bridge piers and replace them with new piers, and it is necessary to reinforce the existing piers in order to satisfy the seismic design requirements against extremely large earthquake motions. Generally known methods of seismic reinforcement for existing RC piers include the steel plate wrapping method and the RC wrapping method, but these methods themselves do not provide the existing RC piers with the seismic performance required for extremely large earthquake motions. On the other hand, if a construction method that satisfies the seismic design requirements for extremely large earthquake motions can be established by utilizing the construction techniques and procedures adopted in the steel plate wrapping method and the RC wrapping method, it will be possible to effectively utilize existing construction equipment and, since no special burden will be placed on construction engineers, it will suddenly become a reality to impart seismic resistance to the extremely large earthquake motions by reinforcing the existing RC piers. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2001-295220 A [Patent Document 2] JP 2002-349011 A Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention aims to solve the above-mentioned problems and achieve the following objectives: That is, the present invention aims to provide a hierarchically reinforced RC pier with hierarchical strength that ensures seismic performance against the design earthquake motion for the existing RC pier while preventing the bridge's function from being impaired even against the extremely large earthquake motion, and a design method thereof. [Means for solving the problem]

[0007] The means for solving the above problems are as follows. <1> An existing RC pier having a footing portion and a column portion erected on the footing portion and having a smaller diameter than the footing portion; an RC wrapping reinforcement portion formed to form a columnar body together with the column portion and wrapped around the outer periphery of the column portion with a thickness such that the diameter of the column portion is smaller than that of the footing portion; a strength-bearing layered reinforcing bar having a bearing plate fixed to its upper end side forming a flange extending in a direction perpendicular to the height direction of the column portion and hanging down from the bearing plate along the height direction of the column portion with its lower end side embedded in the footing portion; and a hollow portion formed inside the RC wrapping reinforcement portion to accommodate the strength-bearing layered reinforcing bar above the portion embedded in the footing portion in a loosely fitted state, the upper side of the hollow portion being a large hollow section having an opening diameter larger than that of the lower section and accommodating the bearing plate, the lower surface of the large hollow section facing the lower surface of the bearing plate, and a hollow sheath formed at a height above the plastic hinge section of the column section when the side portion of the RC wrapping reinforcement section is pulled upward in a manner following the displacement of the side portion of the column section, the large hollow section being a tensile resistance surface that abuts against the lower surface of the bearing plate and resists tensile force, and the large hollow section being formed

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[0008] According to the present invention, it is possible to solve the above-mentioned problems in the conventional technology, and to provide a strength-hierarchical reinforced RC pier with hierarchical strength that ensures seismic performance against the design earthquake motion for the existing RC pier while preventing the bridge's function from being impaired even against the extremely large earthquake motion, and a design method thereof. [Brief description of the drawings]

[0009] [Figure 1] FIG. 2 is a partial cross-sectional view of a strength-bearing layered reinforced RC pier according to the first embodiment. [Diagram 2] This is an enlarged cross-sectional view of a portion of the base of the pier. [Diagram 3] This is a graph showing the stress-strain relationship of concrete in accordance with Highway Bridge Specification V. [Figure 4] This is a diagram showing the stress-strain relationship of axial reinforcement bars in accordance with Highway Bridge Specifications V. [Diagram 5] FIG. 2 is an enlarged partial cross-sectional view of the base of a bridge pier, showing the state when a tensile force is applied due to seismic motion. [Figure 6] FIG. 1 is an explanatory diagram for explaining the expected behavior of the strength-bearing layered reinforced RC pier 1 in the horizontal load-horizontal displacement relationship when subjected to extremely large earthquake motion exceeding the design earthquake motion. [Figure 7(a)] FIG. 2 is an explanatory diagram for explaining the state of a strength-bearing layered reinforced RC pier at the stage of State 1. [Figure 7(b)] FIG. 13 is an explanatory diagram for explaining the state of the strength-bearing layered reinforced RC pier at the stage of State 2. [Figure 7(c)]FIG. 2 is an explanatory diagram for explaining the state of the strength-bearing layered reinforced RC pier in state 3. [Figure 7(d)] FIG. 13 is an explanatory diagram for explaining the state of a bridge pier when it does not have a strength-bearing layered reinforcement bar. [Figure 7(e)] FIG. 13 is an explanatory diagram for explaining the state of the strength-bearing layered reinforced RC pier in state 4. [Figure 8] FIG. 11 is a partial cross-sectional view of a strength-bearing layered reinforced RC pier according to the second embodiment. [Figure 9] This is an enlarged cross-sectional view of a portion of the base of the pier. [Figure 10] FIG. 2 is an enlarged partial cross-sectional view of the base of a bridge pier, showing the state when a tensile force is applied due to seismic motion. [Figure 11] FIG. 1 is a flowchart illustrating an example of a preferred embodiment of a method for designing a strength-reinforced RC pier. [Figure 12(a)] This is a side view of the RC pier (single pier) assumed in the simulation analysis. [Figure 12(b)] This is a cross-sectional view of the superstructure of RC piers (four piers) assumed in the simulation analysis. [Figure 13(a)] This is a diagram showing the specific reinforcement structure on the existing RC pier side. [Figure 13(b)] FIG. 13 is a diagram showing a specific reinforcement structure with the structure of the pier reinforcement added. [Figure 14] FIG. 1 is an explanatory diagram of a multi-mass frame model used in a simulation analysis. [Figure 15] FIG. 1 is a cross-sectional view illustrating modeling of the bridge pier to be designed. [Figure 16] FIG. 13 is a diagram showing the load-displacement relationship applied to a strength-bearing layered reinforcing bar. [Figure 17] FIG. 1 is a diagram showing the stress-strain relationship of concrete set in a simulation analysis. [Figure 18] FIG. 13 is a diagram showing the results of a load increase analysis performed under conditions of gap lengths of 15 mm, 20 mm, and 25 mm. [Figure 19] FIG. 13 is a diagram showing the results of a load increase analysis performed on Cases 1 to 3. [Figure 20]FIG. 13 is a diagram showing the probability distribution of horizontal strength and support fracture strength for Case 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] (Structured reinforced RC piers) The strength-bearing layered reinforced RC pier of the present invention will be described in detail with reference to the drawings.

[0011] [First embodiment] FIG. 1 shows a partial cross-sectional view of a strength-bearing layered reinforced RC pier according to the first embodiment. As shown in FIG. 1, the strength-bearing layered reinforced RC pier 1 comprises an existing RC pier having a footing portion 2a, a column portion 2b erected on the footing portion 2a and having a smaller diameter than the footing portion 2a, and a beam portion 2c arranged on the column portion 2b, a pier reinforcement portion having a wrapping steel plate 3, strength-bearing layered reinforcing bars 4, and anchoring steel 5, and a bridge support portion 10. In the illustrated example, the beam 2c is formed on the top of the column 2b of the existing RC pier, but the present invention also covers, for example, an existing RC pier that does not have a beam 2c. In this case, the bridge support 10 is formed on the column 2b.

[0012] The existing RC pier is an existing RC pier that is the target of reinforcement by the pier reinforcement part, and the existing RC pier itself or the reinforcement of the existing RC pier together with the wrapping steel plate 3 ensures seismic performance up to the design earthquake motion in accordance with the seismic design of the Highway Bridge Specification V. In this sense, there are no particular restrictions on the existing RC pier as long as it is an RC pier of general structure that can ensure seismic performance up to the design earthquake motion in accordance with the seismic design of the Highway Bridge Specifications V, either by itself or by reinforcing it with wrapping steel plate 3, and most existing piers are eligible. In Fig. 1, reference numeral 6 indicates the axial rebars arranged in the existing RC pier, and reference numeral 7 indicates the tie bars bundling the axial rebars. Although not shown, these axial rebars and tie bars are arranged in multiple numbers according to a known RC pier structure. When setting the gap length dx, which will be described later, it is necessary to understand the structure of the existing RC pier, including these axial rebars and tie bars.

[0013] The wrapping steel plate 3 is wrapped around the outer periphery of the column portion 2b to reinforce the existing RC pier. The constituent materials and installation method of the wrapping steel plate 3 are not particularly limited, and can be appropriately selected from known constituent materials and installation methods used in general steel plate wrapping construction methods.

[0014] As shown enlarged in Fig. 2, the load-bearing layered reinforcing bar 4 has a bearing plate 4a fixed to its upper end, which forms a flange extending in a direction (horizontal direction) perpendicular to the height direction (vertical direction) of the column part 2b, and hangs down from the bearing plate 4a along the height direction of the column part 2b, with its lower end embedded in the footing part 2a. Note that Fig. 2 is a partially enlarged cross-sectional view of the pier base. The strength-bearing layered rebar 4 is not particularly limited, and can be appropriately selected from known components and installation methods used in the steel plate winding method, for example, general anchor rebars and their installation methods used in the steel plate winding method. In the illustrated example, the strength-bearing layered rebar 4 is an integrally molded type, but there is no particular limitation as long as it acts as a rebar and has a support plate structure, and for example, a type in which a nut constituting a support plate is screwed onto a rebar with a bolt structure at the top may be used.

[0015] As shown enlarged in Figure 2, the anchoring steel 5 is fixed to the outer surface of the wrapping steel plate 3, and when the side portion of the wrapping steel plate 3 is pulled upward in response to the displacement of the side portion of the column section 2b, a tension resistance plate 5a is formed having a tension resistance surface that abuts against the support plate 4a and resists the tensile force, and the strength-bearing layered reinforcing bar 4 is inserted through the tension resistance plate 5a so as to be able to move forward and backward freely. The constituent materials and installation method of the anchoring steel 5 are not particularly limited and can basically be appropriately selected from known constituent materials and installation methods used in the steel plate winding method, for example, a typical H-shaped steel and its installation method used in the steel plate winding method. In addition, in FIG. 1, in addition to the strength-bearing layered reinforcing bars 4 and anchoring steel 5, strength-bearing layered reinforcing bars 4 and anchoring steel 5 of similar structure are shown in two places, but it is preferable that these strength-bearing layered reinforcing bars and anchoring steel be formed in multiple places at regular intervals around the column portion 2b. In addition, there is no particular restriction on the fixing position of the anchoring steel 5 relative to the wrapping steel plate 3, but since it is reasonable from a construction standpoint to fix it in accordance with the fixing position of the general H-shaped steel used in the steel plate wrapping construction method, it is preferable that it be at a height position equivalent to within the plastic hinge section of the column portion 2b.

[0016] A gap, as described below, is formed between the bearing plates 4a and tensile resistance plates 5a of these strength-bearing layered reinforcing bars 4 and anchoring steel 5. However, if the existing RC pier itself does not satisfy the seismic performance up to the design earthquake motion according to the seismic design of the Highway Bridge Specifications V, then, as with reinforcement using the conventional steel plate wrapping method, the strength-bearing layered reinforcing bars 4 and anchoring steel 5 can be formed without the gap, and the existing RC pier itself and reinforcement using the wrapping steel plate 3 can ensure seismic performance up to the design earthquake motion according to the seismic design of the Highway Bridge Specifications V.

[0017] Regarding the load-bearing layered reinforcing bars 4 and the anchoring steel 5, a new feature not adopted in the above-mentioned steel plate wrapping method is that the gap is formed between the support plate 4a and the tension resistance plate 5a, and the core of the technology in this invention is that the gap length dx, which is the distance between the support plate 4a and the tension resistance plate 5a under normal conditions, is formed so as to satisfy the following formulas (1) and (2). In this specification, the term "normal conditions" refers to a state in which no horizontal displacement due to earthquake motion occurs in the RC reinforced pier.

[0018]

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[0019] The curvature φ in the formula (1) ls ' is the curvature φ as expressed by the formula (2). y and the curvature φ ls3 The curvature φ is set in the range between y and said curvature φ ls3 The concept of will be specifically explained below. First, the φ in the formula (2) y is the curvature that occurs when the pier reaches the limit state 1 specified in the Highway Bridge Specifications V, and is given by the following formula (3) based on the Highway Bridge Specifications V, assuming that the pier is in a state in which the strength-bearing layered reinforcement is not arranged.

[0020]

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[0021] In the formula (3), the bending moment M ls2 , M y0 and φ y0 is calculated by calculating the neutral axis that satisfies the balance condition of the section using the following formulas (4) and (5) under the condition that the fiber strain proportional to the distance from the neutral axis and the stress corresponding to the fiber strain, which are obtained assuming that the plane is maintained, are constant within each infinitesimal element, and then calculating it using the procedure of the following formulas (6) and (7). Note that n is the number of divisions in the section at the pier base, i is the section number representing the pier base divided into n, and j is the element number in the load-bearing direction in the pier base section. Also, the infinitesimal element means a cross-sectional element divided into n at the pier base.

[0022]

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[0023]

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[0024]

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[0025] The strain generated in the axial reinforcing bars arranged on the outermost edge side in the cross section of the pier base is the yield strain ε sy The bending moment and curvature when the bending moment reaches the initial yield bending moment M y0 and initial yield curvature φ y0 The tensile strain of the axial reinforcing bars arranged on the outermost edge side is the tensile strain ε st2 The bending moment when ls2 Let us assume that. Here, ε st2 is given by the following equation (8).

[0026]

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[0027]

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[0028]

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[0029] Next, the φ in the formula (2) ls3 is the curvature that occurs when the pier reaches the limit state 3 specified in the Highway Bridge Specifications V, and is given by the following formulas (14) to (17) based on the Highway Bridge Specifications V, assuming the RC reinforced pier is in a state in which the strength-bearing layered reinforcement bars 4 are not arranged. Here, the φ ls3 (A) The tensile strain of the axial reinforcing bar at the outermost edge of the cross section of the pier base is ε st3 When the compressive strain of the concrete body at the outermost edge of the cross section of the pier base reaches ε ccl Of the two states when the bridge pier reaches this state, the curvature that occurs in the pier in the state that occurs first applies.

[0030]

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[0031] When the gap length dx satisfies the above formulas (1) and (2), the strength-strength hierarchical reinforcement bars 4 will only be activated when the bridge receives an earthquake motion that exceeds Level 2 earthquake motion (the above-mentioned design earthquake motion), and the effect of strength stratification can be obtained, in which the function of the bridge is less likely to be impaired even in the event of the above-mentioned extremely large earthquake motion, due to the activation of the strength-stratification bars 4, while the seismic performance against Level 2 earthquake motion is ensured by structures other than the strength-stratified reinforcement bars 4. In other words, as can be seen from Figure 5, which shows the state when a tensile force is applied due to seismic motion, by appropriately setting the gap length dx based on the above formulas (1) and (2), the strength-bearing hierarchical reinforcing bars 4 will not operate when subjected to an external force of Level 2 seismic motion or less, and only when subjected to seismic motion exceeding Level 2 seismic motion (see arrow A in Figure 5) will the gap be crushed (see arrow B in Figure 5), and the reinforcing bars will operate as load-bearing reinforcing bars.

[0032] Referring again to FIG. A bearing portion 10 is formed in the strength-bearing layered reinforced RC pier 1. The support portion 10 is a member having one end connected onto the existing RC pier, and the other end connected to a superstructure (not shown) so as to be capable of supporting the superstructure. The destructive strength of the support section 10 is set so that it will not be damaged by a horizontal force equivalent to the horizontal strength of the column section 2b when the strength-hierarchical reinforcement bars 4 are not activated, but will be destroyed by a horizontal force equivalent to the horizontal strength that is less than the horizontal strength of the column section 2b that is maximally increased by the activation of the strength-hierarchical reinforcement bars 4. For example, in the illustrated example, the support section 10 is configured with a rubber bearing 13 sandwiched between a base plate 11 and a set plate 12 on the top end of the beam section 2c, and the base plate 11 is fixed to the top end of the beam section 2c with an anchor bolt 14. If the breaking strength of the anchor bolt 14 is set so that it will not be damaged by a horizontal force equivalent to the horizontal strength of the column section when the strength-hierarchized reinforcing bars 4 are not activated, but will be destroyed by a horizontal force equivalent to a horizontal strength less than the horizontal strength of the column section that is maximally increased by the activation of the strength-hierarchized reinforcing bars 4, the beam section 2c and the superstructure will be separated before the strength-hierarchized reinforcing bars 4 yield, and fatal damage such as the bridge collapsing due to the collapse of the pier after the strength-hierarchized reinforcing bars 4 yield can be prevented. The component in which destruction is induced in the support portion 10 may be a set bolt (not shown) connected to the bridge via a rubber bearing 13 or a set plate 12, but among the components of the support portion 10, an anchor bolt 14 is preferred because it has excellent serviceability and recovery ability after destruction. In addition, such a support portion 10 can be formed on the existing RC pier by installing a portion that satisfies the above-mentioned breaking strength setting according to a known construction method. Furthermore, the formation of the support portion 10 for the existing RC pier in which the beam portion 2c does not exist is carried out by the method described above, in which the "beam portion 2c" is replaced with the "column portion 2b".

[0033] The operation of the strength-bearing hierarchically reinforced RC pier 1 constructed as above will be described in more detail with reference to the drawings. FIG. 6 shows the expected behavior of the strength-bearing stratum-reinforced RC pier 1 in terms of the horizontal load-horizontal displacement relationship when subjected to the extremely large earthquake motion exceeding the design earthquake motion. 7(a) to 7(e) show the state of the pier at each stage. In order to show the state of the column 2b of the existing RC pier, the depiction of the pier reinforcement part (wrapping steel plate 3, etc.) arranged to cover the column 2b is omitted.

[0034] When subjected to the extremely large earthquake motion, first, the axial reinforcing bars in the column portion 2b yield (state 1). At the state 1 stage, there is no significant damage in the strength-bearing layered reinforced RC pier 1 (see Fig. 7(a)).

[0035] Next, after reaching state 1, the energy of the earthquake motion is absorbed as the column 2b becomes plastic (state 2). In the strength-bearing hierarchically reinforced RC pier 1 in state 2, damage occurs to the extent that horizontal resistance is not lost due to the plasticization of the column section 2b (see Figure 7(b)).

[0036] Next, after reaching state 2, when the displacement of column section 2b due to the seismic motion exceeds the displacement equivalent to level 2 seismic motion, the gap disappears, the strength-bearing layered reinforcement bars 4 begin to operate, and the load-bearing capacity increases (state 3). In state 3, the strength-layered reinforced RC pier 1 is supported by the strength-layered rebars 4, preventing fatal damage such as the collapse of the pier (Figure 7(c); see Figure 5 for the operating state of the strength-layered rebars 4). At this time, if the strength-bearing layered reinforcement bars 4 are not present or if the strength-bearing layered reinforcement bars 4 do not function, the displacement of the column section 2b will become large, resulting in fatal damage such as the collapse of the pier (see Figure 7(d)).

[0037] Next, after reaching state 3, a state occurs in which the support portion 10 breaks (state 4). In the case of the strength-bearing layered reinforced RC pier 1 in state 4, before the strength-bearing layered rebars 4 yield, the support parts 10 are destroyed and the superstructure is severed, preventing fatal damage such as the collapse of the pier (see Fig. 7(e)). At the same time, the severed superstructure does not deviate from the strength-bearing layered reinforced RC pier 1, preventing fatal damage such as the bridge collapsing (see Fig. 7(e)). In other words, the superstructure, which has been separated from the strength-bearing, hierarchical reinforced RC pier 1 due to the destruction of the support section 10, only transmits the frictional force between the base plate 11 and the top end of the beam section 2c to the strength-bearing, hierarchical reinforced RC pier 1, preventing the collapse of the strength-bearing, hierarchical reinforced RC pier 1. At the same time, the superstructure remains on the strength-bearing, hierarchical reinforced RC pier 1, which has escaped collapse, and does not suffer fatal damage. In the case of the strength-bearing hierarchically reinforced RC pier 1, even if the above-mentioned unforeseeable extremely large earthquake motion occurs, the subsequent collapse scenario can be set as described above, and the effects of the above-mentioned extremely large earthquake motion can be induced to destroy the support parts 10, thereby making it possible to prevent fatal damage such as the bridge falling due to the collapse of the pier, and ultimately making it possible to carry out prompt repairs to restore functionality thereafter.

[0038] It should be noted that in this specification, the terms "states 1 to 4" are to be distinguished from the "limit states 1 to 3" in the Highway Bridge Specifications V. The above-mentioned Highway Bridge Specifications V defines the limit states 1 to 3 as follows: Limit state 1: Elastic limit point on a perfectly elastic-plastic skeleton curve. Limit state 2: The limit state in which the behavior of components etc. becomes irreversible, but the load-bearing capacity can be maintained within the expected range. Limit state 3: The limit state in which the horizontal resistance capacity can be maintained during an earthquake.

[0039] In contrast to this, the above states 1 to 4 show the behavior of an RC pier in which the strength-bearing layered reinforcing bars 4 are arranged, and when explained in relation to the above limit states 1 to 3, they can be explained as follows. State 1: This is the same state as the limit state 1. However, the support 10 is not damaged and the load-bearing layered reinforcing bars 4 are not operating. State 2: A state between the limit states 1 to 3. However, the support 10 is not damaged and the load-bearing layered reinforcing bars 4 are not activated. State 3: This is the state where the load-bearing layered reinforcing bars 4 start to function. However, although it exceeds the limit state 1, it does not exceed the limit state 3. It is preferable that it is about the limit state 2. Also, the support part 10 is not damaged. State 4: The strength of the pier increases due to the actuation of the strength-bearing layered reinforcing bars 4, causing the bearing part 10 to break. However, the limit state 3 has not been reached.

[0040] [Second embodiment] FIG. 8 shows a partial cross-sectional view of a strength-bearing layered reinforced RC pier according to the second embodiment. As shown in Figure 8, the strength-bearing layered reinforced RC pier 20 comprises an existing RC pier having a footing portion 2a, a column portion 2b erected on the footing portion 2a and having a smaller diameter than the footing portion 2a, and a beam portion 2c arranged on the column portion 2b, and a pier reinforcement portion having an RC wrapping reinforcement portion 23, a strength-bearing layered rebar 24, and a hollow portion 25. As in the first embodiment, the present invention also covers the existing RC pier that does not have the beam portion 2c.

[0041] The strength-stratified reinforced RC pier 20 of the second embodiment differs from the strength-stratified reinforced RC pier 1 of the first embodiment in that, instead of the pier reinforcement part made of wrapping steel plate 3, strength-stratified rebar 4 and anchoring steel 5 in the strength-stratified reinforced RC pier 1 of the first embodiment, the pier reinforcement part has an RC wrapping reinforcement part 23, strength-stratified rebar 24 and hollow sheath 25.

[0042] The RC wrapping reinforcement portion 23 is formed so as to form a columnar body together with the column portion 2b, and is wrapped around the outer periphery of the column portion 2b with a thickness such that the diameter of the columnar body is smaller than that of the footing portion 2a. There are no particular limitations on the structure and installation method of the RC wrapping reinforcement portion 23, and they can be appropriately selected from known structures and installation methods employed in general RC wrapping construction methods. In the RC wrapping method, generally, axial reinforcing bars and tie bars are arranged in the reinforcing concrete framework wrapped around the outer periphery of the column 2b to reinforce the existing RC pier. In cases where the existing RC pier itself does not satisfy the seismic performance up to the design earthquake motion according to the seismic design of the Highway Bridge Specifications V, these reinforcing axial reinforcing bars and tie bars can be adopted as optional members to ensure the seismic performance up to the design earthquake motion according to the seismic design of the Highway Bridge Specifications V by reinforcing the existing RC pier itself and the pier reinforcement part.

[0043] As shown enlarged in Fig. 9, the load-bearing layered reinforcing bar 24 has a support plate 4a fixed to its upper end, which forms a flange extending in a direction (horizontal direction) perpendicular to the height direction (vertical direction) of the column part 2b, and hangs down from the support plate 4a along the height direction of the column part 2b, with its lower end embedded in the footing part 2a. Note that Fig. 9 is a partially enlarged cross-sectional view of the pier base. The strength-bearing layered rebar 24 is not particularly limited, and can be appropriately selected from known components and installation methods used in the RC winding method, for example, general anchor rebars and their installation methods used in the RC winding method. In the illustrated example, the strength-bearing layered rebar 24 is an integrally molded type, but there is no particular limitation as long as it acts as a rebar and has a support plate structure, and for example, a type in which a nut constituting a support plate is screwed onto a rebar with a bolt structure at the top may be used.

[0044] As shown enlarged in Figure 9, the hollow sheath 25 is formed as a hollow section that accommodates the strength-bearing layered reinforcing bars 24 above the section embedded in the footing section 2a in a loosely fitted state inside the RC wrapping reinforcement section 23, and the upper side of the hollow section is formed as a large hollow section 25a with a larger opening diameter than the lower section, which accommodates the support plate 24a. The lower portion of the large hollow section 25a faces the lower surface of the support plate 24a and serves as a tensile resistance surface that abuts against the lower surface of the support plate 24a and resists the tensile force when the side portion of the RC wrapping reinforcement section is pulled upward in a manner following the displacement of the side portion of the column section 2b. In addition, the large hollow section 25a of the hollow sheath 25 is formed at a height position above the plastic hinge section (section governed by the length of the plastic hinge length Lp) of the column section 2b so that the strength-bearing layered steel bars 24 will not operate until they receive an earthquake motion exceeding Level 2 earthquake motion (the design earthquake motion). That is, the hollow sheath 25 is formed so that the load-bearing layered reinforcing bars 24 (including the bearing plate 24a) are separated from the RC wrapping reinforcement portion 23 in the plastic hinge section of the column portion 2b. In addition, in FIG. 8, one reinforcement structure made of the multi-layered strength steel bars 24 and the hollow sheaths 25 is shown, however, it is preferable that multiple reinforcement structures made of the multi-layered strength steel bars 24 and the hollow sheaths 25 are formed at regular intervals around the column portion 2b.

[0045] In these strength-bearing layered reinforcing bars 24 and hollow sheaths 25, a gap is formed between the underside of the bearing plate 24a and the underside of the large hollow section 25a, and the strength-bearing layered reinforcing bars 24 are separated from the RC wrapping reinforcement section 23 by the hollow sheaths 25. However, if the existing RC pier itself does not satisfy the seismic performance up to the design earthquake motion according to the seismic design of the Highway Bridge Specifications V, then, as in reinforcement using the conventional RC wrapping method, the upper and lower parts are embedded within these members along the height direction of the column section 2b so as to span between the RC wrapping reinforcement section 23 and the footing section 2a (no gap is set by the hollow sheaths 25), thereby ensuring the seismic performance up to the design earthquake motion according to the seismic design of the Highway Bridge Specifications V by the existing RC pier itself and reinforcement by the RC wrapping reinforcement section 23.

[0046] In the strength-hierarchical reinforced RC pier 20 according to the second embodiment, in order to hierarchically structure the strength of the pier for the design seismic motion and the maximum seismic motion, the gap and the gap length dx can be set in the same manner as in the strength-hierarchical reinforced RC pier 1 according to the first embodiment, and the gap is formed between the bearing plate 24a and the tensile resistance surface (the lower surface of the large hollow portion 25a), and the gap length dx, which is the distance between the bearing plate 24a and the tensile resistance surface under normal conditions, is formed so as to satisfy the above-mentioned equations (1) and (2).

[0047] In other words, by setting the gap and gap length dx in this manner, the strength-hierarchical reinforcement bars 24 will only be activated when the bridge receives an earthquake motion that exceeds Level 2 earthquake motion (the design earthquake motion), and the effect of strength hierarchical reinforcement bars 24 can be obtained, in which the function of the bridge is less likely to be impaired even in the event of the extremely maximum earthquake motion, due to the activation of the strength-hierarchical reinforcement bars 24, while the seismic performance against Level 2 earthquake motion is ensured by structures other than the strength-hierarchical reinforcement bars 24. That is, in the strength-bearing hierarchical reinforced RC pier 20 according to the second embodiment, as can be seen from FIG. 10 which shows the state when a tensile force due to earthquake motion is applied, by appropriately setting the gap length dx based on the above formulas (1) and (2), the strength-bearing hierarchical rebars 24 will not operate when subjected to an external force of Level 2 earthquake motion or less, but will only operate as load-bearing rebars when subjected to earthquake motion exceeding Level 2 earthquake motion (see arrow A in FIG. 10) and the gap is crushed (see arrow B in FIG. 10). However, in the strength-bearing layered reinforced RC pier 20 according to the second embodiment, since the RC lining reinforcement part 23 is applied instead of the lining steel plate 3, the gap length dx is set by changing the above formulas (8), (11), and (15) to the following formulas (18), (19), and (21) in which "βsc" in the above formulas (8), (11), and (15) is replaced with "βco". In other words, the spring constant representing the resistance of the cover concrete is replaced with "βco" in the case where the RC lining reinforcement part 23 expressed by the following formula (20) instead of "βsc" in the case where the lining steel plate 3 is applied, and the gap length dx is set. Moreover, based on application of the following formula (20) for "βco", the gap length dx is set without using the above formula (13) for "βsc". That is, in the strength-bearing layered reinforced RC pier 20 according to the second embodiment, the gap length dx is set using the following formula (20) for "βco" instead of the above formula (13) for "βsc".

[0048]

number

[0049]

number

[0050] However, c in the above formula (20) 0 indicates the shortest distance (mm) from the outermost position of the axial reinforcing bar located on the outermost edge side of the part of the concrete structure where the effective length d' of the tie bar for calculating the plastic hinge length Lp is the longest to the outermost edge of the concrete structure. In the calculation based on the formula (20), the "concrete body" refers to the concrete body of the columnar body composed of the column section 2b of the existing pier and the RC lining reinforcement section 23, and the "axial reinforcement" refers to the axial reinforcement in the column section 2b as well as the axial reinforcement in the RC lining reinforcement section 23. In other words, the calculation based on the formula (20) is performed for the columnar body composed of the column section 2b and the RC lining reinforcement section 23.

[0051]

number

[0052] (Design method for strength-bearing layered reinforced RC piers) The design method for strength-bearing layered reinforced RC pier of the present invention is a method for designing the strength-bearing layered reinforced RC pier of the present invention, and includes at least a curvature calculation step, a distance calculation step, a plastic hinge length calculation step, and a gap setting step, and preferably further includes any steps that are carried out as necessary, such as a support setting step.

[0053] The curvature calculation step is to calculate the curvature φ in the plastic hinge section of the column portion (2b) caused by the displacement caused by the level 2 earthquake motion when the strength-bearing layered reinforcement bar (2, 24) is not activated. ls This is a step of calculating `` In the curvature calculation process, the displacement and the plastic hinge section caused by the level 2 earthquake motion are calculated in advance for the existing RC pier in a state in which the strength-bearing layered reinforcement bar that can be set based on the Highway Bridge Specification V is not present, and the curvature φ in the plastic hinge section caused by the displacement is calculated. ls This can be done by calculating The displacement and the curvature φ ls There is no particular limitation on the method for calculating ', and an example of such a method is to apply fiber elements to the plastic hinge section in a known load incremental analysis method for a multi-mass frame model. In addition, an example of a method for calculating the plastic hinge section is the method described in the Highway Bridge Specifications V. The Level 2 earthquake motion required for the calculation includes earthquake motions specified in the aforementioned Highway Bridge Specifications V, such as 2-II-II-1, NS components on the ground within the JR West Takatori Station premises, etc. In addition, in the case where the seismic performance of the existing RC pier itself is insufficient and the seismic performance up to the design earthquake motion according to the seismic design of the Highway Bridge Specifications V is secured by the reinforcement of the pier reinforcement part, the existing RC pier is replaced with one having the same seismic performance as the state reinforced by the pier reinforcement part, and various calculations are performed. In other words, as the existing RC pier whose insufficient seismic performance is compensated for by the pier reinforcement part, a pier that satisfies the seismic performance up to the design earthquake motion according to the seismic design of the Highway Bridge Specifications V by itself is assumed, and various calculations are performed for the pier related to this assumption. This assumption can be made by taking into consideration the known data of the seismic performance of the existing RC pier after reinforcement obtained from past construction examples using the known steel plate wrapping method or RC wrapping method, and the existing RC pier having the seismic performance equivalent to this known data. This assumption is also applied to the subsequent processes.

[0054] The distance calculation step is performed by calculating the curvature φ ls The shortest distance y from the position of the neutral axis of the column section in the plastic hinge section to the arrangement position of the strength-bearing layered reinforcement bar facing across the central axis of the column section when ' is shown ls This is a step of calculating `` In the distance calculation process, the curvature φ ls The position of the neutral axis in the plastic hinge section when the load-bearing layer reinforcement bar is placed without changing the position of the neutral axis is calculated in advance, and the shortest distance y from the position of the neutral axis to the position of the load-bearing layer reinforcement bar facing each other across the central axis of the column section is calculated. ls This can be done by calculating The method for calculating the neutral axis is not particularly limited, and an example of such a method is to apply a fiber element to the plastic hinge section in a known load increase analysis method for a multi-mass frame model.

[0055] The plastic hinge length calculation step is a step of calculating a plastic hinge length Lp, which is the length of the plastic hinge section. The plastic hinge length calculation process can be carried out by calculating the length of the plastic hinge section caused by level 2 earthquake motion for the existing RC pier in a state in which the strength-bearing layered reinforcement bars are not present. The method for calculating the length of the plastic hinge section is not particularly limited, and may be, for example, the method described in the Highway Bridge Specifications V.

[0056] The gap setting step is performed by setting the curvature φ ls ', the shortest distance y ls This is a process of setting the gap length dx so as to satisfy the following expressions (1) and (2) based on the calculation results of the plastic hinge length Lp and the above-mentioned.

[0057]

number

[0058] The support setting process is a process of setting the destructive strength of the support so that it will be destroyed by a horizontal force that exceeds a horizontal force equivalent to the horizontal strength of the column when the strength-hierarchical reinforcement is not activated, and is less than the horizontal strength of the column that is maximally increased by the activation of the strength-hierarchical reinforcement. The support setting process can be carried out by calculating the horizontal strength of the existing RC pier, and then calculating the maximum horizontal strength of the strength-hierarchical reinforced RC pier when the strength-hierarchical reinforcement is activated with the pier reinforcement part placed without changing the setting, that is, with the strength-hierarchical reinforcement placed. The method of calculating the horizontal strength of the existing RC pier is not particularly limited, and examples of the method include known methods such as the load increase analysis method for a multi-mass frame model using the fiber elements. The method of calculating the maximum horizontal strength when the strength-hierarchized reinforcing bars are activated is not particularly limited, and examples of the method include a method in which the strength-hierarchized reinforcing bars are set not to resist on the compression side and are replaced with "spring elements" of a trilinear model set to resist only after a certain displacement occurs on the tension side in the load increase analysis method for a multi-mass frame model using the fiber elements. In the strength-strength-hierarchical reinforced RC pier designed by the support setting process, the support and the superstructure are disconnected before the strength-strength-hierarchical rebars yield, making it possible to prevent fatal damage such as the bridge falling due to the collapse of the columns accompanying the yielding of the strength-strength-hierarchical rebars. In addition, in each of the above steps, if the calculation target can be used as known data for the existing RC pier, the known data may be used without performing calculations, and in this specification, "calculation" includes the concept of "acquisition" (of known data).

[0059] Below, a preferred embodiment of a design method for the strength-bearing layered reinforced RC pier, taking into account the collapse scenario of the strength-bearing layered reinforced RC pier (see Figures 6, 7, etc.), will be described in detail with reference to Figure 11.

[0060] <1. Setting the collapse scenario> 1.1 Determining the cross section of the pier The cross section of the pier is designed to satisfy the verification for each of the governing conditions for permanent action, fluctuating action, and accidental action shown in the Highway Bridge Specifications V. Here, the pier is assumed to be a flexural failure type pier shown in the Highway Bridge Specifications V.

[0061] 1.2 Design of bearing In accordance with the above-mentioned Highway Bridge Specifications V, the horizontal force acting on the support part is calculated, and the support part is designed so as to satisfy the load-bearing capacity against the horizontal force.

[0062] 1.3 Setting the destruction mode of the support After determining the number and diameter of the anchor bolts in accordance with the Highway Bridge Specifications V, the characteristic value of the breaking strength of the anchor bolts is calculated. When the anchor bolt of the support part is the component in which the destruction is induced, the cross section, etc. are set taking into account the variation in the destruction strength of each component so that the destruction of the rubber bearing, set bolt, etc. of the support part does not precede the breakage of the anchor bolt.

[0063] 1.4 Setting of pier strength after activation of strength-layered reinforcing bars Taking into consideration the destructive strength of the member in which the destruction is induced and the variation in the horizontal resistance of the pier, the horizontal resistance of the pier after the strength-hierarchical reinforcing bars are activated is set.

[0064] 1.5 Confirmation of bridge pier destruction mode It is ensured that no other failure modes precede the failure-induced member. For example, there is a shear failure of the bridge pier. If the characteristic value of the shear resistance of the bridge pier is lower than the destructive strength of the member in which the failure is induced, the bridge pier will reach shear failure before the member in which the failure is induced is destroyed, so the cross section of the pier and the reinforcement arrangement will be reviewed.

[0065] <2. Design of multi-layered strength reinforcement bars> 2.1 Load ramp analysis using fiber elements In order to set the gap between the above-mentioned multi-layered strength rebars, an analysis is performed using fiber elements for the above-mentioned existing RC pier. In this analysis, the cross section of the above-mentioned pier determined in "1.1 Determining the cross section of the pier" is modeled. A load increase analysis is used to calculate the load-displacement relationship of the pier and the bending moment-curvature relationship of the plastic hinge section.

[0066] 2.2 Setting of strength-layered rebar arrangement The reinforcement position of the strength-bearing layered reinforcing bars is set. The position of the strength-bearing layered reinforcement is set at the outer periphery of the column, taking into consideration the clearance with respect to the axial reinforcement set in "1.1 Determination of the cross section of the pier" in accordance with the Highway Bridge Specifications V.

[0067] 2.3 Setting guideline values ​​for gap length of strength-strength layered reinforcing bars A guideline value for the gap length dx of the strength-layered reinforcing bar is set. The curvature and neutral axis position of the plastic hinge section at the displacement that activates the strength-layered reinforcing bar are extracted from the analysis results in "2.1 Implementing a load increase analysis using fiber elements." The gap length dx is calculated from the extracted curvature and neutral axis position and the calculated plastic hinge length according to formula (1). If the strength of the strength-strength-layered reinforcement increases below the displacement of the pier caused by Level 2 earthquake motion, energy absorption through plastic deformation cannot be expected, and the design made in "1.1 Determination of the pier cross section" may no longer be valid. Therefore, the gaps of the strength-strength-layered reinforcement are determined so that the strength-strength-layered reinforcement does not operate up to the displacement caused by Level 2 earthquake motion.

[0068] 2.4 Setting the parameters of strength-layered reinforcement bars The number, diameter, specifications, etc. of the hierarchical strength rebars are set so as to satisfy the horizontal strength of the pier set in "1.4 Setting of pier strength after activation of hierarchical strength rebars".

[0069] <3 Design Review> A load ramp analysis is carried out using the above-mentioned strength-layered rebar as a model. The analysis model is the model created in "2.1 Performing a load ramp analysis using fiber elements" with the above-mentioned strength-layered rebar added. The strength-layered rebar is modeled as a spring element with a gap. Based on the results of the load increase analysis of the model that reflects the above-mentioned strength-strength hierarchical reinforcement, the following three points are examined to confirm whether the above-mentioned collapse scenario is valid. First, confirm whether the strength-layered reinforcement bar operates at a displacement equal to or less than that caused by a Level 2 earthquake motion. This can be confirmed by checking the load-displacement curve of the load increase analysis. If the strength-layered reinforcement bar operates at a displacement equal to or less than the target displacement, review the gap length dx of the strength-layered reinforcement bar. Secondly, check the horizontal strength of the pier after the strength-layered rebars are activated. If the horizontal strength set in "1.4 Setting the pier strength" is not achieved, review the number, diameter, specifications, etc. of the strength-layered rebars. Third, check whether the pier exceeds limit state 3 before reaching the fracture resistance of the member in which the required fracture is induced. If it does, review the number, diameter, or gap length dx of the strength-resistance layered rebars.

[0070] According to the design method of the present invention configured as described above, it is possible to design the strength-reinforced RC pier with hierarchical strength, which ensures seismic performance against the design earthquake motion while preventing overall loss of functionality even against the extremely large earthquake motion, and has hierarchical strength. In addition, based on the collapse scenario, it is possible to design the strength-bearing hierarchical reinforced RC pier, which can prevent fatal damage such as the collapse of the bridge due to the collapse of the pier by inducing failure to the components where failure is induced, and which can then be quickly repaired to restore functionality. EXAMPLES

[0071] In order to confirm the effectiveness of the strength-bearing layered reinforced RC pier and its design method of the present invention, the following simulation analysis was carried out.

[0072] <Simulation target> In the above simulation analysis, the existing RC pier shown in Figures 12(a) and (b) was assumed as a typical example. This existing RC pier was an RC pier that does not meet the load-bearing performance shown in Reference 1 below. Note that Figure 12(a) is a side view of the RC pier (single pier) assumed in the simulation analysis, and Figure 12(b) is a cross-sectional view of the superstructure of the RC pier (four piers) assumed in the simulation analysis. In the simulation analysis, the existing RC pier is extracted as the design target pier, and an analysis is performed on the single-leg RC pier. Reference 1: Japan Road Association: Reference material for seismic reinforcement of existing road bridges, 1997.

[0073] The pier to be designed was a pier that was reinforced by wrapping steel plates around the strength-bearing hierarchical reinforced RC pier of embodiment 1. The specific reinforcement structure on the existing RC pier side was the reinforcement structure shown in Figure 13(a), and the specific reinforcement structure with the structure of the pier reinforcement part added was the reinforcement structure shown in Figure 13(b). As shown in Figure 13(a), the existing RC pier side will have a reinforced structure using axial reinforcement, tie bars and assembly bars, which are necessary to ensure load-bearing capacity against Level 2 earthquake motion. Also, as shown in 13(b), in order to ensure a horizontal strength equivalent to that of the reinforcement shown in Reference 1, on the pier reinforcement side, reinforcing bars (anchor bars, material: SD345, reinforcing bar diameter: D41) are arranged around the steel material (wrapped steel plate) and H-shaped steel (not shown) via the steel material, and the strength-layered reinforcing bars that operate when the displacement corresponding to level 2 earthquake motion is exceeded are arranged around the steel material via the steel material and the H-shaped steel. At this time, only the strength-layered reinforcing bars are arranged with the gap between the support plate and the tensile resistance plate of the H-shaped steel. In addition, SD490 reinforcing bars are used for the strength-layered reinforcing bars in order to ensure sufficient horizontal strength in a limited arrangement space, and the reinforcing bar diameter is set to D51. The specific specifications of the materials used for the existing RC pier are shown in Table 1 below, and the specifications of the materials used for the pier reinforcement are shown in Table 2 below.

[0074] [Table 1]

[0075] [Table 2]

[0076] <Simulation conditions> The simulation analysis was performed using TDAPIII (a general-purpose three-dimensional dynamic analysis program for civil engineering and construction, manufactured by Ark Information Systems Co., Ltd.). The analysis method used was displacement-controlled incremental load analysis. The loading conditions in the analysis were set to allow loading of the existing RC pier after reinforcement up to a displacement equal to or greater than the limit state 3, and the loading method was set to apply a displacement of 0.01 mm / step to the top of the pier, which is the position where the inertial force acts.

[0077] A multi-mass frame model was used as the analytical model. A specific multi-mass frame model is shown in Figure 14. As shown in Figure 14, the multi-mass frame model for the design target pier is modeled with the plastic hinge section as a "fiber element", the column section above the plastic hinge section as a "linear beam element", and the beam section as a "linear beam element (rigid member)". The column base, which is the lower end of the column, is fixed, and the footing and foundation located at a height below the column base are not modeled.

[0078] In addition, the strength-bearing layered rebars in the pier reinforcement were modeled as "spring elements." That is, the strength-bearing layered rebars are set as nonlinear "spring elements" that resist only axial tension because they only begin to resist axial tension once a certain displacement is reached due to the gap. In this case, the strength-layered reinforcement bar was modeled only in the plastic hinge section at the position where it is actually placed in the cross section as shown in Figure 15. The reason for modeling the strength-layered reinforcement bar at the position where it is actually placed in the cross section, unlike the reinforcing bar (anchor reinforcement bar), is that the timing of the strength increase is determined by the distance from the strength-layered reinforcement bar to the neutral axis, and the reason for modeling only the plastic hinge section is that the deformation amount in the section of the "linear beam element" above the plastic hinge section does not affect the displacement at which the strength-layered reinforcement bar operates. By performing such modeling, the response displacement of the strength-layered reinforcement bar can be accurately grasped. Moreover, the strength-bearing layered reinforcing bars were modeled as "spring elements" by giving them the load-displacement relationship shown in FIG. In addition, the load-displacement relationship of the gap before the strength-bearing layered reinforcing bars act and after the strength-bearing layered reinforcing bars yield is set to 10 -5 It is set with a small gradient of about kN / m.

[0079] The stress-strain relationship of the concrete in the modeled "fiber element" was set based on the above-mentioned Reference 1 by converting the cross-sectional area of ​​the steel material (wrapped steel plate) into a hoop reinforcing bar as the reinforcing effect of the steel material. However, in the stress-strain relationship of the concrete, the limit compressive strain ε ccl In the above strain range, strain ε c is the maximum compressive stress σ cc The strain ε when cc from the limit compressive strain ε ccl Even after the stress drops to 0.0N / mm, the downward slope continues. 2 The stress-strain relationship of the concrete set in the simulation analysis is shown in FIG.

[0080] <Simulation results> In order to verify the gap length dx of the strength-bearing layered reinforcing bars, the load increase analysis was carried out with gap lengths dx of 15 mm, 20 mm, and 25 mm. Here, the conditions of 15 mm and 20 mm satisfy the above-mentioned formulas (1) and (2) regarding the setting of the gap length dx, and the condition of 25 mm (gap length dx is long) does not satisfy the above-mentioned formulas (1) and (2).

[0081] The results of the load increase analysis are shown in Figure 18. The vertical axis in the figure shows the horizontal strength (load) of the design pier, and the horizontal axis shows the displacement at the top of the design pier. In addition to the analysis results for each gap condition, the figure also shows the displacement limit values ​​considered to be limit states 2 and 3 for the design pier.

[0082] Under the condition that the gap length dx is 25 mm, the displacement of the top of the pier on which the strength-layered reinforcing bars act (the horizontal strength increases) is about 135 mm, and it is confirmed that the strength-layered reinforcing bars act as reinforcing bars that bear the load after exceeding the displacement considered to be limit state 3. In this simulation, the decrease in horizontal strength (load) of the design target pier is not shown because the decrease in horizontal strength after exceeding the displacement considered to be limit state 3 is not modeled, but it has been confirmed through experiments, etc. that the horizontal strength (load) of an actual pier drops sharply and collapses when limit state 3 is exceeded. Therefore, when subjected to earthquake motion exceeding level 2 earthquake motion, it is shown that the design target pier collapses before the destruction part moves to the support part, and the collapse scenario described above does not hold.

[0083] On the other hand, under the condition that the gap length dx is 15 mm, the displacement of the pier top where the strength-layered reinforcing bars act (the horizontal strength increases) is about 90 mm, and it is confirmed that the strength-layered reinforcing bars start to function before reaching the displacement regarded as limit state 2, and start to function as reinforcing bars that bear the load before reaching the displacement regarded as limit state 3. Although not shown, under these conditions the strength-layered reinforcing bars start to function after reaching the displacement regarded as limit state 1.

[0084] Furthermore, when the gap length dx is set to 20 mm, the displacement of the top of the pier on which the strength-hierarchical reinforcement acts (the horizontal strength increases) is approximately 110 mm, and it has been confirmed that the strength-hierarchical reinforcement begins to function as a load-bearing reinforcement before the displacement considered to be limit state 3 is reached. Therefore, this shows that under the conditions that satisfy the above-mentioned equations (1) and (2) regarding the setting of the gap length dx, it is possible to induce the effect of earthquake motion exceeding level 2 earthquake motion to cause the destruction of the above-mentioned support parts before reaching the displacement regarded as limit state 3, which means that it is possible to induce a scenario that is less likely to lead to the collapse of the bridge as a whole.

[0085] In addition to the design pier (case 1) with the gap length dx set to 20 mm, the load increase analysis was also performed on a design pier (case 0) with the existing RC pier (see Figure 13(a)) without reinforcement as a condition, and a design pier (case 2) with reinforcement but without modeling the strength-bearing layered reinforcement bars (without the "spring element" in Figure 14).

[0086] The analysis results of the load increase analysis for these are shown in Figure 19. The vertical axis in the figure shows the horizontal resistance (load) of the design pier, and the horizontal axis shows the displacement at the top of the pier. In addition to the analysis results for each gap condition, the figure also shows the limit values ​​of displacement considered to be limit states 2 and 3 for the design pier.

[0087] In Case 0, a decrease in horizontal strength (load) was confirmed before reaching the displacement considered to be limit state 2, and it was confirmed that the seismic performance against the design earthquake motion according to the seismic design of the Highway Bridge Specification V was not satisfied. In Case 2, no such decrease in horizontal strength (load) was observed, and it was confirmed that the seismic performance required for the seismic design of the Highway Bridge Specification V was satisfied up to the design earthquake motion. Case 1 behaves similarly to Case 2 up to limit state 2. After that, as shown in Figure 18, it is confirmed that the horizontal resistance (load) increases beyond limit state 2 before reaching limit state 3.

[0088] Next, for Case 1, Figure 20 shows the probability distribution of the horizontal strength (load) when the variation in the horizontal strength of the pier is assumed to be an exceedance probability of 5% both before and after the strength increase, and the fracture strength of the support part (anchor bolt) when the exceedance probability is also assumed to be 5%. As shown in Figure 20, if the fracture strength of the support part (anchor bolt) is, for example, 3,620 kN, within the set range of exceedance probability of 5%, the support part will not fracture before the strength of the pier increases, and will fracture after the strength of the pier increases. Therefore, the intended collapse scenario can be realized while giving the design target pier reliability up to an exceedance probability of 5%. [Explanation of symbols]

[0089] 1. Strength-reinforced RC piers with layered structure 2a Footing 2b Pillar part 2c Beam section 3. Wrapped steel plate 4,24 Strength-bearing layered reinforcement 4a,24a Support plate 5. Fixing Steel 5a Tensile resistance plate 6 Axial reinforcement 7. Tie-down Reinforcement 8. Tie-down Reinforcement 10 Bearing part 11 Base plate 12 set plates 13 Rubber bearing 14 Anchor bolt 23 RC winding reinforcement 25 Hollow sheath 25a Large hollow part

Claims

1. An existing RC pier having a footing portion and a column portion erected on the footing portion and having a smaller diameter than the footing portion; The RC wrapping reinforcement is formed to form a columnar body together with the column, and is wrapped around the outer periphery of the column with a thickness such that the diameter of the columnar body is smaller than that of the footing, a support plate is fixed to the upper end of the support plate forming a flange that protrudes in a direction perpendicular to the height direction of the column, and the support plate hangs down from the support plate along the height direction of the column and the lower end side is embedded in the footing, and the support plate is fixed to the upper end of the support plate and the lower end side of the support plate is embedded in the footing, and the support plate is fixed to the upper end of the support plate. a hollow sheath formed as a hollow section for accommodating a reinforcing bar in a loosely fitted state, the upper side of said hollow section being a large hollow section with a larger opening diameter than the lower section for accommodating the support plate, the lower surface of said large hollow section facing the lower surface of said support plate, so as to come into contact with the lower surface of said support plate to act as a tensile resistance surface that resists tensile force when the side surface of said RC wrapping reinforcement section is pulled upward in a manner following the displacement of the side surface of said column section, and said large hollow section being formed at a height position exceeding the plastic hinge section of said column section; A bridge support portion disposed on the existing RC pier; A strength-bearing layered reinforced RC pier characterized in that a gap is formed between the bearing plate and the tensile resistance surface under normal conditions, and the gap length dx, which is the distance between the bearing plate and the tensile resistance surface, is formed so as to satisfy the following equations (1) and (2). [0010] In the above formulas (1) and (2), φ ｌｓ ' represents the curvature in the plastic hinge section of the column caused by the displacement caused by the level 2 earthquake motion, and y ｌｓ ' is the curvature φ ｌｓ ' indicates the shortest distance from the position of the neutral axis of the column part in the plastic hinge section to the arrangement position of the strength-bearing layered reinforcing bar facing across the central axis of the column part, Lp indicates the plastic hinge length, which is the length of the plastic hinge section, and φ y indicates the curvature at the displacement considered as limit state 1 of the bridge pier as specified in the Highway Bridge Specifications V, and φ ｌｓ３ indicates the curvature at the displacement considered to be the limit state 3 of the pier as specified in the Highway Bridge Specifications V.

2. 2. The strength-hierarchized reinforced RC pier according to claim 1, wherein the destructive strength of the support part is set so that it will not be damaged by a horizontal force equivalent to the horizontal strength of the column part when the strength-hierarchized reinforcement bar is not activated, but will be destroyed by a horizontal force equivalent to the horizontal strength that is less than the horizontal strength of the column part that is maximally increased by the activation of the strength-hierarchized reinforcement bar.

3. A method for designing a strength-bearing layered reinforced RC pier according to any one of claims 1 to 2, At least, the curvature φ in the plastic hinge section of the column caused by the displacement caused by the level 2 earthquake motion when the strength-bearing layered reinforcement is not activated ｌｓ A curvature calculation step of calculating '; The curvature φ ｌｓ The shortest distance y from the position of the neutral axis of the column part in the plastic hinge section to the arrangement position of the strength-bearing layered reinforcement bar facing across the central axis of the column part when ' is shown ｌｓ a distance calculation step of calculating '; A plastic hinge length calculation step of calculating a plastic hinge length Lp, which is the length of the plastic hinge section; The curvature φ ｌｓ ', the shortest distance y ｌｓ a gap setting process of setting the gap length dx so as to satisfy the following formulas (1) and (2) based on the calculation results of the plastic hinge length Lp, A design method for a strength-bearing layered reinforced RC pier, comprising: [0025] In the above formulas (1) and (2), φ ｌｓ ' represents the curvature in the plastic hinge section of the column caused by the displacement caused by the level 2 earthquake motion, and y ｌｓ ' is the curvature φ ｌｓ ' indicates the shortest distance from the position of the neutral axis of the column section to the arrangement position of the strength-bearing layered reinforcing bar facing across the central axis of the column section in the plastic hinge section, Lp indicates the plastic hinge length, which is the length of the plastic hinge section, and φ y indicates the curvature at the displacement considered as limit state 1 of the bridge pier as specified in the Highway Bridge Specifications V, and φ ｌｓ３ indicates the curvature at the displacement considered to be the limit state 3 of the pier as specified in the Highway Bridge Specifications V.

4. The design method for a strength-hierarchized reinforced RC pier according to claim 3 further includes a support setting step of setting the destructive strength of the support so that the pier will not be damaged by a horizontal force equivalent to the horizontal strength of the column when the strength-hierarchized reinforcement is not activated, but will be destroyed by a horizontal force equivalent to the horizontal strength that is less than the horizontal strength of the column that is maximally increased by the activation of the strength-hierarchized reinforcement.

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